A short python code to understand the use of context managers in python (with statement)

context_managers_in_py.py

#below is the class based context manager

class ContextTest:

    def __init__(self) -> None:
        print("initialized the ContextManager")
    
    def __enter__(self) -> None:
        print("entered into the with block")

    def __exit__(self,exc_type,exc_value,exc_traceback) -> None:
        print(exc_type,exc_value,exc_traceback)
        print("excited the with block")
    
with ContextTest() as manager:
    print("inside the with")


#decorator based context manager
from contextlib import contextmanager

@contextmanager
def write_something(name):
    try:
        print("entered the with block")
        yield name
    finally:
        print("exited the with block")

with write_something("hello") as name:
    print("inside the with block:",name)


#a bullet point manager (a fun implementation of with statement)

class BulletList:

    def __init__(self)->None:
        self.intend = 0
    
    def __enter__(self):
        self.intend += 1
        return self
    
    def __exit__(self,exc_type,exc_value,exc_traceback) -> None:
        self.intend -= 1
    
    def bulletType(self) -> str:
        types = ["o ","- ","* "]
        return types[self.intend%3]
    
    def item(self,text)-> None:
        print(" "*self.intend + self.bulletType() + text)

with BulletList() as bullet:
    bullet.item("hello")
    with bullet:
        bullet.item("world")
        bullet.item("python")
    with bullet:
        bullet.item("is awesome")
        with bullet:
            bullet.item("and so is you")
            bullet.item("and so is me")
        
        bullet.item("and so is we all")
        with bullet:
            bullet.item("and so is you and me")
            bullet.item("and so is me and all")
    
    bullet.item("and so is we all and us")

class TesingWith:

    def __init__(self) -> None:
        self.num = 0
    
    def __enter__(self):
        self.num += 1
        return self
    
    def __exit__(self,exc_type,exc_value,exc_traceback) -> None:
        self.num -= 1
    
    def display(self) -> None:
        print(self.num)


with TesingWith() as t:
    t.display()
    with t:
        t.display()
        with t:
            t.display()
            with t:
                t.display()
                with t:
                    t.display()
                    with t:
                        t.display()
                        with t:
                            t.display()
                            with t:
                                t.display()
                                with t:
                                    t.display()
                                    with t:
                                        t.display()
                                    t.display()
                                t.display()
                            t.display()
                        t.display()
                    t.display()
                t.display()
            t.display()
        t.display()
    t.display()
t.display()